Circulation

fluid flow

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Alternative Title:
overturn

Figure 2: Annual circulation patterns in a dimictic lake. The typical dimictic lake undergoes stratification in the summer and complete overturn in the autumn and spring. During winter, surface ice prevents further mixing by the wind. Small differences in density and temperature exist, with cooler water (0° C) staying near the surface and warmer, more dense water (4° C) extending to the bottom.

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estuaries

...where salt water is measurably diluted with fresh water. On average, estuaries are biologically more productive than either the adjacent river or the sea, because they have a special kind of water
circulation that traps plant nutrients and stimulates primary production. Fresh water, being lighter than salt water, tends to form a distinct layer that floats at the surface of the estuary. At the...

fluid dynamics

The proof of Thomson’s theorem depends on the concept of
circulation, which Thomson introduced. This quantity is defined for a closed loop which is embedded in, and moves with, the fluid; denoted by
K, it is the integral around the loop of
v ·
dl, where
dl is an element of length along the loop. If the vorticity is...

hydrology of the Dead Sea

...warmer than the layers beneath it, it did not sink. By the winter of 1978–79, however, the upper-level layer had become cool and saturated enough to sink, setting off an event known as an overturn (a mixing of the water layers). Since then the trend has been toward restoring the formerly stratified water layers, but with more instances of overturning.

lake stratification

...and the mixing effects of wind (Figure 2). This type of lake stratifies in summer as the surface water (epilimnion) warms and ceases to mix with the lower, colder layer (hypolimnion). Water circulates within but not between the layers, more vigorously within the epilimnion. The boundary between these layers is the metalimnion, a zone of rapid temperature change. With the onset of...

Mixing due to cooling or warming processes that increase the density of surface waters sufficiently to cause them to sink results in what is termed
circulation, or overturn, of lake waters. Lakes that cool to below 4 °C in winter experience two turnover periods, as just described, and are called dimictic lakes. Most lakes in temperate regions fall into this category. Lakes that do not cool...

During the fall a lake is cooled at its surface, the surface water sinks, and convective overturn proceeds as the density of the surface water increases with the decreasing temperature. By the time the surface water reaches 4 °C (39.2 °F), the temperature of maximum density for fresh water, the density-driven convective overturn has reached the bottom of the lake, and overturn ceases....